Changes in respiratory system resistance and reactance following acute respiratory and metabolic alkalosis in dogs

To differentiate between the effects of respiratory and metabolic alkalosis on respiratory mechanics, respiratory system resistance (Rrs) and reactance (Xrs) were examined in anesthetized, paralyzed, and mechanically hyperventilated dogs. Rrs and Xrs were measured by the forced oscillation method with a random noise input of 0-25 Hz. Restoration to normocapnia by CO₂ inhalation significantly increased Rrs (+23.4±4.0%), particularly at high-frequency ranges without alterations in Xrs or resonant frequencies, whereas an increase in pH without changes in partial pressure of arterial carbon dioxide (PaCO ₂) by an administration of bicarbonate-carbonate mixture resulted in no significant alteration in Rrs or Xrs. A significant decrease in Rrs (-16.3±2.5%) following vagotomy or atropine administration was no longer affected by CO₂ inhalation. These results suggest that (1) the vagus nerve appears to play a role in maintaining the resting tension of airway smooth muscle, (2) systemic hypocapnia decreases Rrs presumably due to the central airway dilation, and (3) this response is associated with a change in systemic partial pressure of carbon dioxide (PCO ₂) rather than that in pH.